The invention relates to fluorescent screens and more particularly to fluorescent screens for use as X-ray intensifying screens.
X-ray intensifying screens are usually mounted in pairs on opposing sides of an X-ray film for purposes of enhancing the exposure of said film. This enhancement is achieved due to the relatively high efficiency of the screens in converting X-ray energy into electromagnetic radiation within the ultraviolet (UV) and visible spectrums. Screens of this variety usually consist of a support layer, a reflectance layer, and a fluorescent layer. When employed in the paired relationship described, the fluorescent layers are normally positioned in contact with the opposing sides of the X-ray film to form a "casette". A protective layer is typically provided over the fluorescent layer to facilitate removal of stains, dust, dirt, and other undesirable matter from the screen's surface.
In typical intensifying screens of the known prior art, both the reflectance material, e.g. pigments of magnesium oxide or titanium dioxide, and the phosphors employed as the fluorescent material were dispersed in organic polymeric binders and deposited during separate operations on the supportive layer. Because of this practice of using an organic binder, recovery and recycling of the phosphor materials from defective and other unused screen pieces has been exceedingly difficult. Normally, such a recovery process involves soaking the scrap pieces in a solvent such as acetone to dissolve the organic binder. Agitation is then utilized to assist in "peeling-off" the phosphors. Subsequent steps typically include filtering and drying of the phosphors. Heretofore, analyses of phosphors recovered using the above method indicated the presence of either the magnesium oxide or titanium dioxide within the range of from about 0.5 to 5 percent. When recovered phosphors having said relatively high ranges for these non-luminescent diluents were subsequently utilized in the formation of new screens, an undesirable compromise in screen quality resulted. This condition also existed when the recovered phosphors were blended with virgin phosphor materials. On some occasions, it was necessary to scrap the recovered phosphors. This situation in turn presented an economical problem to the screen industry, particularly with the recent introduction of newer, more expensive X-ray phosphors such as those of the rare earth variety.
It is believed therefore that a fluorescent screen which eliminates the necessity for employment of an organic polymeric binder as an integral part of the reflectance layer typically used in such screens would constitute an advancement in the art.
It is further believed that a new method for making a screen of the variety described would constitute an art advancement. As will be understood by the following detailed description, the screen of the present invention possesses the desired features of relatively low lag (persistence) and increased speed (brightness) over fluorescent screens of the prior art.